This invention relates to a rotary seal assembly for preventing fluid leakage between a shaft of a rotating machine and a fixed housing through which the shaft passes. The seal of the invention is particularly suited to applications where solid-containing or corrosive fluids, such as the slurries commonly encountered in mineral processing operations, are being pumped, but it also finds application with less difficult liquids.
In conventional clear liquid pumping applications stuffing boxes or packed glands are commonly used to provide the required seal. With seals of this type, there is rapid wear, especially if a slurry is pumped, and a continuous requirement for large volumes of high pressure clean gland service water.
In another type of seal assembly commonly used, there is a sealing element arranged on the shaft and another sealing element which is non-rotatable. The sealing element on the shaft is biased towards the stationary element by a spring, usually in the form of an annular bellows. The problem with known arrangements of this sort, when used in slurry pumping applications, is that the bellows is exposed to the pumped slurry with the result that it clogs up and its operation is hampered. It is for this very reason that the bellows is attached to the rotating sealing element so that the movement of the bellows assists somewhat in freeing it from fouling. In slurry pumping operations using known seals of this sort, the slurry also has access to the sealing surfaces of the elements, with the result that they wear quickly. To counter this, service water is injected continuously at high pressure directly into the vicinity of the sealing elements to keep them free of slurry. Where the pump's operating pressure is, say, 4 bar, the injected water may have to have a pressure of around 18 bar. Besides the disadvantage that very high pressure water is required, a great volume of water is wasted with continuous injection and undesired dilution of the pumped liquid takes place. If the high pressure supply of service water should fail, or should its pressure drop, as commonly happens in practice, rapid wear of the sealing surfaces takes place as the slurry abrades them. In the conventional arrangements, the sealing surfaces are all arranged to be at right angles to the pump axis, and it is believed that this configuration enhances the rapid wear which takes place under such conditions.
It is an object of this invention, at least in some embodiments, to alleviate the problems outlined above.